This invention pertains to a source substructure for use in field-emission-type, ion-beam generating devices.
In the recent past, this field of art has experienced widespread and growing interest in the use of so-called field-emission-type focused ion beams. Such beams are used for a number of purposes, such as for the micromachining of certain materials, for implantation of ions in the making of semiconductor devices, and in a number of other applications.
Generically speaking, in a typical liquid-metal ion source substructure there is a needle-like device, on the tip of which, during operation, is supported a film of a selected liquid metal fuel, or metal alloy, from which ions are emitted under the action of an intense, applied electrical field.
With respect to such a substructure, there are a number of important considerations. For example, many of the highly desirable metal fuels for liquid ions, such as fuels containing boron, are extremely corrosive to many potential source substructure materials, and it is important, therefore, to try to maximize corrosion resistance in order to have a substructure which offers a long useful lifespan. Another consideration is that a substructure should be designed in such a manner that it offers a high degree of power efficiency, so that a relatively low amount of power is required to heat the fuel properly to create the required liquid-metal melt pool. Desirable also is a substructure which is designed in such a fashion that it has a high fuel-holding capacity so that extended operating times are possible before metal replenishment is required.
In addition to these important considerations are also the following. The source substructure should offer a fairly high degree of rigidity in order to operate predictably and reliably with the usual associated electro-optical focusing apparatus. Further, the substructure should be as simple and inexpensive as possible.
A general object of the present invention, therefore, is to provide a unique liquid-metal ion-source substructure which takes all of the above-mentioned important considerations and requirements into account in a highly practical and satisfactory manner.
Thus, an object of the invention is to provide such a substructure which staunchly resists corrosion by ion-beam fuel materials, which requires extremely low power levels for proper operation, and which offers, as another significant contributor to long operating life cycles, a high fuel-metal holding capacity.
A further object of the invention, taking into account the considerations recited above, is to provide a substructure of the type generally outlined which is rigid, simple and extremely inexpensive.
According to a preferred embodiment of the invention, the proposed substructure takes the form of an elongate carbon needle which is tapered to a point at one end, and which is structurally supported entirely within the turns of an electrical contacting heating coil which has end leads that are conductively connected to and structurally supported by a pair of relatively large cross section electrical feeder legs. At least one, and preferably plural, elongate groove(s) extend along the length of the needle and into the tapered region to form significant reservoir space for enabling the substructure to hold a large quantity of metal source material.
These and other significant advantages and features which are offered by the substructure of the present invention will become more fully apparent as the description that now follows is read in conjunction with the accompanying drawings.